1. Field of the Invention
The present invention relates to a novel circumferential gap seal for axial-flow machines.
In modern axial-flow machines (turbines or compressors) with their high pressure ratios, when giving consideration to the relatively short blade lengths, particularly stringent requirements are set in connection with the maintenance of small radial gaps between the rotor blade tips and the encompassing casing components, so as to ensure the required high degree of efficiency during all operating conditions. Due to unequal thermal and/or mechanical loading, the casing and rotors may be exposed to differing expansions under varying operating conditions, such as start, accelaration and shutdown or rundown whereby the radial gaps will, in essence, when the gaps become wider, the efficiency reduces, when they become narrower, this presents the danger of rubbing or fracture, particularly when the casing is distorted out of true round, in effect, assumes a polygonal or oval configuration.
2. Discussion of the Prior Art
Heretofore, attempts have been made to maintain the specified size of the circumferential gap under particular operating conditions (for example, start) by directed, intermittent blowing against the casings. However, this measure has proven itself as being inadequate both with regard to its effectiveness as well as long term applicability.